Good Day to everyone...

Hi, Im just a newbie here. I would like to ask for your help in programming the Siemens S7 - 200 and OP3.

I just would like to ask if there is a program block in Siemens s7-200 that can detect power failure or no supply to the plc itself. Because when power failure occurs, the plc still continue to supply power to the OP3 because of its battery, so the OP3 still continue to count and give input to the plc. But the program inside of the PlC already stop working. So when power resume to the plc, the OP3 have already bypassed important operation. That's my main problem, how to stop OP3 in giving input value to the plc when there is power failure.

Please help me. Thank you very much.

P.S.
If you want to see the program, I can provide you. Thanks again

Hi ,

I think you should build up a "Fail-Safe" design. If you are still insterested in it, let's talk more detail.

If you need a cheap decision, remake the cable to connect an external 24V supply (pins 7 and 2)
see http://support.automation.siemens.com/WW/l...cedownload=true at page 15-4

Best regards

Hi Good Day!

Sir,

I am not allowed to make any configuration on the hardware part of the OP3. So what i can do only is to change the program inside of the s7-200 plc. So is it possible to do that.

Thanks

Late reply but you can use the first scan or Run Power up bit to determine if the PLC has restarted

First_Scan_On SM0.1 This bit is ON for the first scan cycle only. One use is to call an initialization subroutine.

or RUN_Power_Up SM0.3 This bit is turned ON for one scan cycle when RUN mode is entered from a power-up condition. This bit can be used to provide machine warm-up time before starting an operation.

You would have to program what you wanted to do on startup, you could clear the registers or set an alarm or stop your process, whatever.

Cheers